A conventional pipe for transporting liquids or soft, viscous material (hereinafter collectively termed "liquids" for simplicity) is designed for simply transporting liquid phase materials. However, some liquids transported through a pipe are apt to degenerate due to gases such as air dissolved in the liquid. For example, ultra demineralized water used in manufacturing integrated circuit type semiconductors and solutions used for liquid chromatography are unsuitable for their intended purpose if air is dissolved in the liquid. As a consequence, a deaerator unit or a deaerator tower must be incorporated into such a liquid production process or such a liquid transportation piping system to remove the gas such as air from the liquid before the liquid is transferred through the pipe into a container or transported to a destination. However, installing a deaerator unit or a deaerator tower in a liquid production process or in a liquid transportation system requires a great deal of investment in terms of equipment costs as well as a large installation space.